Clock synchronizing method of a multiple clock domain memory device

ABSTRACT

A memory device includes: a first clock receiver configured to receive a first clock signal; a second clock receiver configured to receive a second clock signal when data is input or output, wherein the second clock signal has a first clock frequency in a preamble period, and has a second clock frequency different from the first clock frequency after the preamble period; a command decoder configured to receive a clock synchronization command synchronized with the first clock signal and generate a clock synchronization signal, wherein the clock synchronization signal is generated during the preamble period; and a clock synchronizing circuit configured to generate a plurality of division clock signals in response to the second clock signal, latch the clock synchronization signal during the preamble period, and selectively provide the plurality of division clock signals as internal data clock signals according to a result of the latching.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2016-0129872, filed on Oct. 7, 2016, in the KoreanIntellectual Property Office, the disclosure of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The inventive concept relates to a memory device, and more particularly,to a memory device that performs a clock synchronizing operation byusing a clock signal having a dynamic frequency.

DISCUSSION OF RELATED ART

Dynamic random access memory (DRAM) may receive a command and an addressin synchronization with a main clock signal CK. The DRAM may alsoreceive or transmit data in synchronization with a data clock signalWCK. A DRAM performs two main operations. These include an operation ofwriting data in a memory cell array included in a core circuit and anoperation of reading the data from the memory cell array. Controlsignals, which are generated to control the core circuit based on themain clock signal CK, and data, which is input/output to/from the corecircuit based on the data clock signal WCK, are supplied in differentclock domains. Therefore, the DRAM synchronizes the main clock signal CKand the data clock signal WCK so that input/output data can be stablylatched in response to the control signals. As an operation frequency ofthe DRAM increases, an aligning margin of a setup time or a hold time isreduced when synchronizing the main clock signal CK and the data clocksignal WCK. Accordingly, these signals may not be synched with eachother.

SUMMARY

An exemplary embodiment of the inventive concept provides a memorydevice including a first clock receiver configured to receive a firstclock signal; a second clock receiver configured to receive a secondclock signal when data is input or output, wherein the second clocksignal has a first clock frequency in a preamble period, and has asecond clock frequency different from the first clock frequency afterthe preamble period; a command decoder configured to receive a clocksynchronization command synchronized with the first clock signal andgenerate a clock synchronization signal, wherein the clocksynchronization signal is generated during the preamble period; and aclock synchronizing circuit configured to generate a plurality ofdivision clock signals in response to the second clock signal, latch theclock synchronization signal during the preamble period, and selectivelyprovide the plurality of division clock signals as internal data clocksignals according to a result of the latching.

An exemplary embodiment of the inventive concept provides a memorydevice including: a data clock receiver configured to receive a dataclock signal when data is input or output, wherein the data clock signalhas a first clock frequency in a preamble period before a time when thedata is input or output, and has a second clock frequency different fromthe first clock frequency after the preamble period; a command decoderconfigured to receive a clock synchronization command to generate aclock synchronization signal during the preamble period; and a clocksynchronizing circuit configured to divide the data clock signal andgenerate a plurality of division clock signals, latch the clocksynchronization signal in response to a division clock signal selectedfrom among the plurality of division clock signals, and selectivelyoutput the plurality of division clock signals as internal data clocksignals according to a result of the latch.

An exemplary embodiment of the inventive concept provides a clocksynchronizing method performed by a memory device, the clocksynchronizing method including: receiving a first clock signal;receiving a second clock signal which has a first clock frequency in apreamble period before a time when data is input or output, and has asecond clock frequency different from the first clock frequency afterthe preamble period; receiving a clock synchronization commandsynchronized with the first clock signal and generating a clocksynchronization signal during the preamble period; dividing the secondclock signal and generating a plurality of division clock signals;latching the clock synchronization signal in response to a divisionclock signal selected from among the plurality of division clocksignals; and selectively outputting the plurality of division clocksignals as internal data clock signals according to a result of thelatching.

An exemplary embodiment of the inventive concept provides a memorydevice including: a first clock receiver configured to receive a firstclock signal; a second clock receiver configured to receive a secondclock signal, wherein the second clock signal has a first frequency in afirst period and a second frequency in a second period after the firstperiod; a command decoder configured to generate a clock synchronizationsignal in the first period in response to a command; and a clocksynchronizing circuit configured to divide the second clock signal intoa plurality of divided clock signals and output the divided output clocksignals as internal data clock signals in response to the clocksynchronization signal.

An exemplary embodiment of the inventive concept provides a memorydevice including: a first clock receiver configured to receive a firstclock signal; a second clock receiver configured to receive a secondclock signal, wherein the second clock signal has a first frequency in afirst period and a second frequency in a second period after the firstperiod; a command decoder configured to generate a clock synchronizationsignal in the first period in response to a command; and a clocksynchronizing circuit configured to divide the second clock signal intoa plurality of divided clock signals and output the divided output clocksignals as internal data clock signals in response to the clocksynchronization signal.

An exemplary embodiment of the inventive concept provides a memorydevice including: a main clock receiver configured to receive a mainclock signal and generate an internal main clock signal; a data clockreceiver configured to receive a data clock signal; a command decoderconfigured to receive an instruction from a memory controller and togenerate an internal synchronization signal in response to theinstruction; and a clock synchronizing circuit configured to receive thedata clock signal buffered through the data clock receiver and theinternal synchronization signal to perform a clock synchronizationoperation in which an internal data clock signal is generated, whereinthe internal synchronization signal has a high level during a preambleperiod of the main clock signal.

An exemplary embodiment of the inventive concept provides a methodincluding: receiving a main clock signal; receiving a data clock signal;receiving a clock synchronizing command and generating an internal clocksynchronization signal; generating first, second, third and fourthdivided data clock signals based on the data clock signal; comparing theinternal clock synchronization signal with the second divided data clocksignal and generating a first phase detection signal, and comparing theinternal clock synchronization signal with the fourth divided data clocksignal and generating a second phase detection signal; and synchronizingthe main clock signal and the data clock signal by using first, second,third and fourth internal data clock signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the inventive concept will be moreclearly understood by describing in detail exemplary embodiments thereofwith reference to the accompanying drawings in which:

FIG. 1 is a diagram for describing a memory system including a multipleclock domain memory device according to an exemplary embodiment of theinventive concept;

FIG. 2 is a timing diagram for describing a conventional high speed datainterface operation of the memory device of FIG. 1;

FIGS. 3 and 4 are diagrams for describing a conventional clocksynchronizing operation of the memory device of FIG. 1;

FIGS. 5A and 5B are timing diagrams for describing a data clock signalhaving a dynamic frequency according to an exemplary embodiment of theinventive concept;

FIG. 6 is a diagram for describing a multiple clock domain memory deviceaccording to an exemplary embodiment of the inventive concept;

FIG. 7 is a diagram for describing a clock synchronizing circuit of FIG.6 according to an exemplary embodiment of the inventive concept;

FIGS. 8A and 8B are diagrams for describing first and second phasedetectors of FIG. 7 according to an exemplary embodiment of theinventive concept;

FIG. 9 is a diagram for describing a multiplexer of FIG. 7 according toan exemplary embodiment of the inventive concept;

FIGS. 10 and 11 are timing diagrams for describing an operation of aclock synchronizing circuit of FIG. 7 according to an exemplaryembodiment of the inventive concept;

FIG. 12 is a flowchart of a clock synchronizing operation performed by amemory device of FIG. 6 according to an exemplary embodiment of theinventive concept; and

FIG. 13 is a block diagram illustrating an example wherein a memorysystem for performing a clock synchronizing operation according toexemplary embodiments of the inventive concept is applied to a computingsystem.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a diagram of a memory system 100 including a multiple clockdomain memory device according to an exemplary embodiment of theinventive concept.

Referring to FIG. 1, the memory system 100 may include a memorycontroller 110 and a memory device 120. The memory system 100 maysupport data communication between the memory controller 110 and thememory device 120 and uses a main clock signal CK and a data clocksignal WCK.

A first clock signal line 11, a command bus 12, an address bus 13, asecond clock signal line 14, and a data bus 15 may be connected betweenthe memory controller 110 and the memory device 120. According to anexemplary embodiment of the inventive concept, the memory system 100 maysupport the data communication based on various clock signals inaddition to the main clock signal CK and the data clock signal WCK.

The main clock signal CK generated by the memory controller 110 may besupplied to the memory device 120 through the first clock signal line11. For example, the main clock signal CK may be supplied as acontinuous alternating inversion signal along with an inversion mainclock signal CKB. Regarding a main clock signal pair CK and CKB,rising/falling edges may be detected with respect to an intersectionpoint of the main clock signal CK and the inversion main clock signalCKB, and thus, a timing accuracy is increased. Herein, the main clocksignal CK may be referred to as a first clock signal CK.

According to an exemplary embodiment of the inventive concept, a singlemain clock signal CK may be supplied as the continuous alternatinginversion signal to the first clock signal line 11. In this case, todistinguish the rising/falling edges of the main clock signal CK, themain clock signal CK is compared with a reference voltage Vref. However,when noise fluctuation and/or the like occurs in the reference voltageVref, a shift occurs in detecting the main clock signal CK, and thus,the timing accuracy is reduced compared to a case of using a main clocksignal pair CK and CKB.

Therefore, the first clock signal line 11 may transmit a complementarycontinuous alternating inversion signal based on the main clock signalpair CK and CKB. In this case, the first clock signal line 11 mayinclude two signal lines for transmitting the main clock signals CK andCKB. The clock signal CK described herein may refer to the main clocksignal pair CK and CKB.

A command CMD and an address ADDR supplied from the memory controller110 may be supplied to the memory device 120 through the command bus 12and the address bus 13, respectively. According to an exemplaryembodiment of the inventive concept, the command CMD and the addressADDR may be supplied to the memory device 120 through a sharedcommand/address bus. The command CMD or the address ADDR may betime-serially delivered along the shared command/address bus.

The data clock signal WCK and data DQ may be transmitted to a datainterface between the memory controller 110 and the memory device 120.The data clock signal WCK generated by the memory controller 110 may besupplied to the memory device 120 through the second clock signal line14. The data clock signal WCK may be supplied as a continuousalternating inversion signal along with an inversion data clock WCKB.Regarding a data clock signal pair WCK and WCKB, rising/falling edgesmay be detected with respect to an intersection point of the data clocksignal WCK and the inversion data clock signal WCKB, and thus, a timingaccuracy is increased.

The second clock signal line 14 may transmit a complementary continuousalternating inversion signal based on the data clock signal pair WCK andWCKB. In this case, the second clock signal line 14 may be configured toinclude two signal lines for transmitting the data clock signals WCK andWCKB. The data clock signal WCK described herein may refer to the dataclock signal pair WCK and WCKB. Herein, the data clock signal WCK may bereferred to as a second clock signal WCK.

The data DQ synchronized with the data clock signal WCK may betransmitted through the data bus 15 connected between the memorycontroller 110 and the memory device 120. For example, write data DQ,which corresponds to a burst length BL and is supplied from the memorycontroller 110, may be transmitted to the memory device 120 through thedata bus 15 in synchronization with the data clock signal WCK. The writedata DQ, which corresponds to the burst length BL and is read from thememory device 120, may be latched in synchronization with the data clocksignal WCK and may be transmitted to the memory controller 110 throughthe data bus 15.

Accordingly, a data interface speed between the memory controller 110and the memory device 120 increases.

If, however, the memory device 120 is implemented with DRAM, a corecircuit of the DRAM may not operate according to a speed of a high speeddata interface. In other words, there is a limitation in increasing afrequency of the main clock signal CK transmitted to the core circuit ofthe DRAM. Therefore, the DRAM may use a method of increasing a datainterface speed while maintaining an operation speed of the core circuitof the DRAM.

FIG. 2 is a timing diagram for describing a conventional high speed datainterface operation of the memory device of FIG. 1.

Referring to FIG. 2 and FIG. 1, the main clock signal CK may betransmitted from the memory controller 110, and the command CMD and theaddress signal ADDR may be transmitted based on the main clock signalCK. The data DQ may be transmitted based on the data clock signal WCK.For a high speed data interface, a frequency of the data clock signalWCK may be set to be twice the frequency of the main clock signal CK.

It is assumed that a data writing operation is performed in the memorydevice 120. The memory device 120 may receive the main clock signal CKfrom a time T1 and may receive a write command CMD and a write addresssignal ADDR based on the main clock signal CK at a time T2. In addition,at the time T2, the memory device 120 may receive the write data DQcorresponding to the burst length, based on the data clock signal WCK.

In reference to FIG. 2, the memory device 120 is described as receivingthe write command CMD and the write data DQ at the time T2. It is to beunderstood, however, that the memory device 120 may receive the writecommand CMD, and then, may receive the write data DQ after a writelatency. The write latency may be represented as a multiple of a cycleof the main clock signal CK.

In reference to FIG. 2, it is also assumed that a data reading operationis performed in the memory device 120. The memory device 120 may receivethe main clock signal CK from the time T1 and may receive a read commandCMD and a read address signal ADDR based on the main clock signal CK atthe time T2. In addition, after the read command CMD is received, thememory device 120 may receive read data DQ based on the data clocksignal WCK after a read latency. The read latency may be represented asa multiple of the cycle of the main clock signal CK.

In a write operation, the memory device 120 may sample the data DQ inputfrom the memory controller 110 by using the data clock signal WCK, andmay store data, obtained through the sampling, in a memory cell array byusing the main clock signal CK. In addition, in a read operation, thememory device 120 may read the data from the memory cell array by usingthe main clock signal CK and may transmit the read data to the memorycontroller 110 by using the data clock signal WCK. As described above,the memory device 120 may operate in different clock domains, forexample, a multiple clock domain.

In the memory device 120, data transfer is performed between a domainwhich operates based on the main clock signal CK and a domain whichoperates based on the data clock signal WCK. In other words, domaincrossing occurs between the main clock signal CK and the data clocksignal WCK, and in this case, missing data may occur. To prevent missingdata, a clock synchronizing operation between the main clock signal CKand the data clock signal WCK is performed. The clock synchronizingoperation between the main clock signal CK and the data clock signal WCKwill be described below with reference to FIGS. 3 and 4.

FIGS. 3 and 4 are diagrams for describing a conventional clocksynchronizing operation in the memory device of FIG. 1. FIG. 3 is fordescribing an aligned state in which clock synchronization between themain clock signal CK and the data clock signal WCK takes place. FIG. 4is for describing a misaligned state in which clock synchronization doesnot take place.

Referring to FIG. 3, the main clock signal CK and the data clock signalWCK may be received by the memory device 120 (see FIG. 1). A frequencyof the data clock signal WCK may be higher than that of the main clocksignal CK. For example, a frequency of the data clock signal WCK may betwice a frequency of the main clock signal CK.

The main clock signal CK may be received from a time T1. A falling edgeof the main clock signal CK may be input at the time T1, a rising edgeof the main clock signal CK may be input at a time T2, a falling edge ofthe main clock signal CK may be input at a time T3, a rising edge of themain clock signal CK may be input at a time T4, and a falling edge ofthe main clock signal CK may be input at a time T5.

The data clock signal WCK may be received from the time T2. Since thedata clock signal WCK is supplied along with corresponding data DQwhenever the write data DQ is input or the read data DQ is output, thedata clock signal WCK may be in a deactivation state at the time T1, andthen, may be activated at the time T2 when the corresponding data DQ issupplied. In other words, unlike the main clock signal CK, which isalways supplied, the data clock signal WCK may be supplied when it isneeded so that power consumption may be reduced.

When the data clock signal WCK is received at the time T2, the memorydevice 120 may divide the data clock signal WCK to generate a pluralityof divided data clock signals WCK_0, WCK_90, WCK_180, and WCK_270. Inthis case, the memory device 120 may twice-divide the data clock signalWCK to generate the plurality of divided data clock signals WCK_0,WCK_90, WCK_180, and WCK_270. Frequencies of the divided data clocksignals WCK_0, WCK_90, WCK_180, and WCK_270 may be the same as that ofthe main clock signal CK.

From the time T2 when the data clock signal WCK is received, a firstdivided data clock signal WCK_0 may be generated to have the same phaseas that of the main clock signal CK, a second divided data clock signalWCK_90 may be generated to have a phase obtained through a 90-degreeshift from a phase of the main clock signal CK, a third divided dataclock signal WCK_180 may be generated to have a phase obtained through a180-degree shift from the phase of the main clock signal CK, and afourth divided data clock signal WCK_270 may be generated to have aphase obtained through a 270-degree shift from the phase of the mainclock signal CK.

As shown in FIG. 3, with regard the first divided data clock signalWCK_0, at the time T2, a rising edge of the first divided data clocksignal WCK_0 may correspond to a rising edge of the main clock signalCK. At the time T3, a falling edge of the first divided data clocksignal WCK_0 may correspond to a falling edge of the main clock signalCK. At the time T4, a rising edge of the first divided data clock signalWCK_0 may correspond to the rising edge of the main clock signal CK. Inaddition, at the time T5, a falling edge of the first divided data clocksignal WCK_0 may correspond to the falling edge of the main clock signalCK.

The memory device 120, for example, may have an align margin including asetup time S of 0.25tCK and a hold time H of 0.25tCK when determining afalling edge of the first divided data clock signal WCK_0 at the timeT3. The memory device 120 may determine a logic level of the firstdivided data clock signal WCK_0 in response to a falling edge of themain clock signal CK, based on the setup time S of 0.25tCK and the holdtime H of 0.25tCK. When the determined logic level of the first divideddata clock signal WCK_0 is logic low, the memory device 120 maydetermine the first divided data clock signal WCK_0 as having a fallingedge.

The setup time S of 0.25tCK and the hold time H of 0.25tCK at the timeT3 may be an ideal align margin. Here, tCK denotes a clock cycle periodof the main clock signal CK. However, in designing the memory device120, an align margin capable of being actually applied may be strictlyapplied. For example, the align margin may be defined as the setup timeS of 0.25tCK and the hold time H of 0.25tCK.

Due to the setup time S of 0.25tCK and the hold time H of 0.25tCK whichare strictly defined, the align margin can become insufficient whendetermining a rising edge of the first divided data clock signal WCK_0.Thus, a clock synchronizing operation of the memory device 120 may notwork.

In FIG. 3, it can be seen that a rising edge of the first divided dataclock signal WCK_0 corresponds to the rising edge of the main clocksignal CK, and a falling edge of the first divided data clock signalWCK_0 corresponds to the falling edge of the main clock signal CK.Furthermore, the second divided clock signal WCK_90 has a high level atT3. This shows an aligned state in which clock synchronization takesplace between the main clock signal CK and the data clock signal WCK. Onthe other hand, FIG. 4 shows a misaligned state wherein clocksynchronization does not take place between the main clock signal CK andthe data clock signal WCK.

Referring to FIG. 4, as in FIG. 3, the memory device 120 may receive themain clock signal CK and the data clock signal WCK and may divide thedata clock signal WCK to generate a plurality of divided data clocksignals WCK_0, WCK_90, WCK_180, and WCK_270.

Regarding a first divided data clock signal WCK_0 in FIG. 4, at a timeT2 when the data clock signal WCK is received, a falling edge of thefirst divided data clock signal WCK_0 may be generated unlike a risingedge of the main clock signal CK. At a time T3, a rising edge of thefirst divided data clock signal WCK_0 may be generated unlike a fallingedge of the main clock signal CK. At a time T4, a falling edge of thefirst divided data clock signal WCK_0 may be generated unlike the risingedge of the main clock signal CK. In addition, at a time T5, a risingedge of the first divided data clock signal WCK_0 may be generatedunlike the falling edge of the main clock signal CK.

Regarding FIG. 4, it can be seen that a falling edge of the firstdivided data clock signal WCK_0 is generated in the rising edge of themain clock signal CK, and a rising edge of the first divided data clocksignal WCK_0 is generated in the falling edge of the main clock signalCK. Furthermore, the second divided clock signal WCK_90 has a low levelat T3. This shows a misaligned state in which clock synchronization doesnot take place between the main clock signal CK and the data clocksignal WCK.

For example, at the time T3, to determine that the first divided dataclock signal WCK_0 is generated as a rising edge with the falling edgeof the main clock signal CK, the memory device 120 may determine a logiclevel of the first divided data clock signal WCK_0 in response to afalling edge of the main clock signal CK, based on a setup time S of0.25tCK and a hold time H of 0.25tCK. When the determined logic level ofthe first divided data clock signal WCK_0 is logic high, the memorydevice 120 may determine the first divided data clock signal WCK_0 ashaving a rising edge.

Similarly to FIG. 3, the setup time S of 0.25tCK and the hold time H of0.25tCK at the time T3 may be an ideal align margin. However, an alignmargin capable of being actually applied may be strictly applied. Forexample, the align margin may be defined as the setup time S of 0.25tCKand the hold time H of 0.25tCK. In this case, due to the insufficiencyof the align margin caused by to the setup time S of 0.25tCK and thehold time H of 0.25tCK, which are strictly defined, a clocksynchronizing operation of the memory device 120 may not work.

In an exemplary embodiment of the inventive concept, a method ofperforming the clock synchronizing operation by using the data clocksignal WCK having a variable frequency (e.g., a dynamic frequency) isused to correct for the insufficiency of the align margin in the clocksynchronizing operation.

FIGS. 5A and 5B are timing diagrams for describing a data clock signalhaving a dynamic frequency according to an exemplary embodiment of theinventive concept.

Referring to FIG. 5A, the main clock signal CK and the data clock signalWCK may be received by the memory device 120 (see FIG. 1). The dataclock signal WCK may have a preamble period before a time when the dataDQ is input/output. The data clock signal WCK may be set to have avariable frequency so that a frequency of the preamble period and afrequency of a data input/output period are set to be different fromeach other. In other words, the data clock signal WCK may be set to havea dynamic frequency.

The main clock signal CK may be received from a time Ta. A falling edgeof the main clock signal CK may be input at the time Ta, a rising edgeof the main clock signal CK may be input at a time Tb, a falling edge ofthe main clock signal CK may be input at a time Tc, a rising edge of themain clock signal CK may be input at a time Td, and a falling edge ofthe main clock signal CK may be input at a time Te. The main clocksignal CK may have a clock cycle period of tCK.

The data clock signal WCK may be received from the time Tb. The dataclock signal WCK may have a preamble period from the time Tb to the timeTd and may be supplied as a continuous alternating inversion signal fromthe time Td. The data clock signal WCK may be set to have one clockcycle period of tCK identical to the frequency of the main clock signalCK during the preamble period. The data clock signal WCK may be set totwice the frequency of the main clock signal CK from the time Td afterthe preamble period.

According to an exemplary embodiment of the inventive concept, the dataclock signal WCK may be set to have a preamble period having variousfrequencies. For example, the preamble period of the data clock signalWCK may be set to one tCK clock cycle period, or may be set to n (wheren is a natural number equal to or more than two) number of tCK clockcycle periods. Alternatively, the preamble period of the data clocksignal WCK may be set to n (where n is a natural number equal to or morethan two) number of tCK/2 clock cycle periods.

After the preamble period of the data clock signal WCK, the data DQ maybe transmitted based on the data clock signal WCK. For example, the dataDQ may be transmitted based on the data clock signal WCK at the time Teafter one clock cycle “tWCK” of the data clock signal WCK from the timeTd after the preamble period.

As another example, as shown in FIG. 5B, the data DQ may be transmittedbased on the data clock signal WCK at a time Ti after a plurality ofclock cycles “tWCK” of the data clock signal WCK from the time Td afterthe preamble period.

In the present embodiment, a transmission time (or an input/output time)of the data DQ based on the data clock signal WCK may be set to a timewhen a data clock signal cycle “tWCK”, for example, an n*tWCK (where nis a natural number equal to or more than one) clock cycle, elapsesafter the preamble period of the data clock signal WCK.

In an exemplary embodiment of the inventive concept, a transmission time(or an input/output time) of the data DQ based on the data clock signalWCK may be set to a time when a half data clock signal cycle “tWCK/2”,for example, an n*tWCK/2 (where n is a natural number equal to or morethan one) clock cycle, elapses after the preamble period of the dataclock signal WCK.

Hereinafter, a memory device for performing a clock synchronizingoperation by using the data clock signal WCK having the dynamicfrequency of FIG. 5 and a clock synchronizing method will be describedin detail with reference to FIGS. 6 to 12.

FIG. 6 is a diagram for describing a multiple clock domain memory device120 according to an exemplary embodiment of the inventive concept.

Referring to FIG. 6, the memory device 120 may include a command decoder610, a main clock receiver 620, a core circuit 630, a data clockreceiver 640, a clock synchronizing circuit 650, and a data circuit 660.

The command decoder 610 may receive a command CMD or CMD_SYNCtransmitted through the command bus 12 (see FIG. 1) from the memorycontroller 110 (see FIG. 1). The command decoder 610 may decode thereceived command CMD to generate an internal command signal ICMD and aclock synchronization signal ISYNC.

The command decoder 610 may generate the internal command signal ICMDincluding a read signal or a write signal according to a received readcommand RD_CMD or write command WR_CMD. The internal command signal ICMDmay be supplied to the core circuit 630. The internal command signalICMD may control a data reading operation or a data writing operationperformed by the core circuit 630.

The command decoder 610 may generate the clock synchronization signalISYNC in response to a received clock synchronization command CMD_SYNCor an internal main clock signal ICK supplied from the main clockreceiver 620. The clock synchronization signal ISYNC may be generated asa pulse signal with a period corresponding to the received clocksynchronization command CMD_SYNC. The clock synchronization signal ISYNCmay be supplied to the clock synchronizing circuit 650.

The main clock receiver 620 may receive the main clock signal CKtransmitted through the first clock signal line 11 (see FIG. 1) from thememory controller 110. The main clock receiver 620 may buffer thereceived main clock signal CK to generate the internal main clock signalICK and may supply the internal main clock signal ICK to the commanddecoder 610 and the core circuit 630. A phase of the buffered internalmain clock signal ICK may be approximately equal to that of the mainclock signal CK.

The core circuit 630 may include a memory cell array 632. In a readoperation of the memory device 120, the core circuit 630 may read datafrom the memory cell array 632 in response to the internal commandsignal ICMD and the internal main clock signal ICK which are readsignals. In a write operation of the memory device 120, the core circuit630 may write data in the memory cell array 632 in response to theinternal command signal ICMD and the internal main clock signal ICKwhich are write signals.

The core circuit 630 may further include a row decoder and a columndecoder which are connected to the memory cell array 632. The memorycell array 632 may include a plurality of memory cells which arearranged in rows and columns. Each of the plurality of memory cells maybe configured with one access transistor and one storage capacitor. Thememory cells may have an arrangement structure in which the memory cellsare disposed near intersection points of a plurality of word lines and aplurality of bit lines forming a matrix.

The row decoder may decode a row address signal ADDR received throughthe address bus 13 (see FIG. 1) and may drive a word line selected fromamong the plurality of word lines connected to the memory cells of thememory cell array 632 according to a decoded row address signal. Thecolumn decoder may decode a column address signal ADDR received throughthe address bus 13 and may perform column gating according to a decodedcolumn address signal to select the bit lines connected to the memorycells of the memory cell array 632.

The data clock receiver 640 may receive the data clock signal WCKtransmitted through the second clock signal line 14 (see FIG. 1) fromthe memory controller 110. The data clock receiver 640 may buffer thereceived data clock signal WCK to supply the buffered data clock signalWCK to the clock synchronizing circuit 650.

The clock synchronizing circuit 650 may receive the data clock signalWCK buffered by the data clock receiver 640 and the clocksynchronization signal ISYNC to perform a clock synchronizing operation.As a result of the clock synchronizing operation, the clocksynchronizing circuit 650 may generate an internal data clock signalIWCK which includes first to fourth internal data clock signalsIWCK/2_0, IWCK/2_90, IWCK/2_180, and IWCK/2_270. The internal data clocksignal IWCK may be supplied to the data circuit 660.

The data circuit 660 may include a data input circuit and a data outputcircuit. In response to the internal data clock signal IWCK, the datainput circuit may align and latch the write data DQ input through thedata bus 15 (see FIG. 1) to supply write data DIN to the memory cellarray 632. In response to the internal data clock signal IWCK, the dataoutput circuit may transmit read data DOUT, read from the memory cellarray 632, as output data DQ to the memory controller 110.

In a write operation, the data circuit 660 may operate so that the writedata DQ input from the memory controller 110 is sampled by using theinternal data clock signal IWCK, and data obtained through the samplingis written in the memory cell array 632 by using the internal main clocksignal ICK. In addition, in a read operation, the data circuit 660 mayoperate so that data is read from the memory cell array 632 by using theinternal main clock signal ICK, and the read data is transmitted to thememory controller 110 by using the internal data clock signal IWCK.

In the memory device 120, since the internal main clock signal ICK andthe internal data clock signal IWCK are synchronized with each other bythe clock synchronizing circuit 650, synchronization may be made betweena domain operating based on the internal main clock signal ICK and adomain operating based on the internal data clock signal IWCK.Therefore, the memory device 120 may perform data communication withoutmissing data in a high speed data interface.

FIGS. 7 to 9 are diagrams for describing the clock synchronizing circuitof FIG. 6, according to an exemplary embodiment of the inventiveconcept. FIGS. 8A and 8B are circuit diagrams for describing first andsecond phase detectors 731 and 732 of FIG. 7, according to an exemplaryembodiment of the inventive concept. FIG. 9 is a circuit diagram fordescribing a multiplexer 740 of FIG. 7, according to an exemplaryembodiment of the inventive concept.

Referring to FIG. 7, the clock synchronizing circuit 650 may divide thedata clock signal WCK to generate a plurality of division clock signalsWCK/2_0, WCK/2_90, WCK/2_180, and WCK/2_270. The clock synchronizingcircuit 650 may generate the internal data clock signal IWCKsynchronized with the internal main clock signal ICK (see FIG. 6), basedon the clock synchronization signal ISYNC. The clock synchronizingcircuit 650 may include a multi-phase generator 720, first and secondphase detectors 731 and 732, and a multiplexer circuit 740. The dataclock signal WCK may be the data clock signal WCK having the dynamicfrequency described above with reference to FIGS. 5A and 5B.

The multi-phase generator 720 may shift a phase of the data clock signalWCK by 0 degrees, 90 degrees, 180 degrees, and 270 degrees by using adivider to generate first to fourth division clock signals WCK/2_0,WCK/2_90, WCK/2_180, and WCK/2_270. For example, the multi-phasegenerator 720 may generate the first to fourth division clock signalsWCK/2_0, WCK/2_90, WCK/2_180, and WCK/2_270 respectively having phasesobtained from 0-degree, 90-degree, 180-degree, and 270-degree phaseshifts of an output of the divider which receives the data clock signalWCK as input.

In response to the second and fourth division clock signals WCK/2_90 andWCK/2_270, each of the first and second phase detectors 731 and 732 maylatch the clock synchronization signal ISYNC to generate first andsecond phase detection signals PDS_90 and PDS_270.

The first phase detector 731, as illustrated in FIG. 8A, may include aflip-flop 810 that latches the clock synchronization signal ISYNC tooutput the first phase detection signal PDS_90 in response to the seconddivision clock signal WCK/2_90. The second phase detector 732, asillustrated in FIG. 8B, may include a flip-flop 820 that latches theclock synchronization signal ISYNC to output the second phase detectionsignal PDS_270 in response to the fourth division clock signalWCK/2_270.

For example, in a case where the first phase detector 731 latches theclock synchronization signal ISYNC in response to the second divisionclock signal WCK/2_90, when a logic level of the latched clocksynchronization signal ISYNC is logic high, the first phase detectionsignal PDS_90 may be generated at a logic high level. This indicatesthat a logic high level of the clock synchronization signal ISYNC isaligned with a rising edge of the second division clock signal WCK/2_90.

According to an exemplary embodiment of the inventive concept, the firstphase detector 731 may capture a logic level of the clocksynchronization signal ISYNC by using a falling edge of the seconddivision clock signal WCK/2_90.

Here, since the clock synchronization signal ISYNC is generated inassociation with the internal main clock signal ICK (see FIG. 6), thesecond division clock signal WCK/2_90 aligned with the clocksynchronization signal ISYNC may be a signal synchronized with theinternal main clock signal ICK. In this case, the second phase detector732 may latch the clock synchronization signal ISYNC to generate thesecond phase detection signal PDS_270 having a logic low level inresponse to the fourth division clock signal WCK/2_270 which is in astate where its phase is inverted by 180 degrees with respect to thesecond division clock signal WCK/2_90.

As another example, when a logic level of the clock synchronizationsignal ISYNC which has been latched by the first phase detector 731 inresponse to the second division clock signal WCK/2_90 is logic low, thefirst phase detection signal PDS_90 may be generated at a logic lowlevel. In this case, the second phase detector 732 may latch the clocksynchronization signal ISYNC to generate the second phase detectionsignal PDS_270 having a logic high level in response to the fourthdivision clock signal WCK/2_270 which is in a state where its phase isinverted by 180 degrees with respect to the second division clock signalWCK/2_90. This indicates that a logic high level of the clocksynchronization signal ISYNC is aligned with a rising edge of the fourthdivision clock signal WCK/2_270, and the fourth division clock signalWCK/2_270 may be a signal synchronized with the internal main clocksignal ICK.

According to an exemplary embodiment of the inventive concept, thesecond phase detector 732 may capture a logic level of the clocksynchronization signal ISYNC by using a falling edge of the fourthdivision clock signal WCK/2_270.

The first and second phase detection signals PDS_90 and PDS_270 may besupplied to the multiplexer 740 of FIG. 9 and may act as control signalsfor generating the internal data clock signals IWCK/2_0, IWCK/2_90,IWCK/2_180, and IWCK/2_270.

Referring to FIG. 9, the multiplexer circuit 740 may include first tofourth multiplexers 910, 920, 930, and 940. The first multiplexer 910may receive the first division clock signal WCK/2_0 through a firstinput terminal I1 and may receive through a second input terminal 12 thethird division clock signal WCK/2_180 which is in a state where itsphase is inverted by 180 degrees with respect to the first divisionclock signal WCK/2_0. The first multiplexer 910 may select one signalfrom among the first division clock signal WCK/2_0 at the first inputterminal I1 and the third division clock signal WCK/2_180 at the secondinput terminal 12 to output the selected signal as the first internaldata clock signal IWCK/2_0 in response to the first and second phasedetection signals PDS_90 and PDS_270.

For example, when the first phase detection signal PDS_90 is at a logichigh level and the second phase detection signal PDS_270 is at a logiclow level, the first multiplexer 910 may select the first division clocksignal WCK/2_0 at the first input terminal I1 to be output as the firstinternal data clock signal IWCK/2_0. On the other hand, when the firstphase detection signal PDS_90 is at a logic high level and the secondphase detection signal PDS_270 is at a logic high level, the firstmultiplexer 910 may select the third division clock signal WCK/2_180 atthe second input terminal 12 to be output as the first internal dataclock signal IWCK/2_0.

The second multiplexer 920 may receive the second division clock signalWCK/2_90 through a first input terminal I1 and may receive through asecond input terminal 12 the fourth division clock signal WCK/2_270which is in a state where its phase is inverted by 180 degrees withrespect to the second division clock signal WCK/2_90. The secondmultiplexer 920 may select one signal from among the second divisionclock signal WCK/2_90 and the fourth division clock signal WCK/2_270 tobe output as the second internal data clock signal IWCK/2_90 in responseto the first and second phase detection signals PDS_90 and PDS_270.

The second multiplexer 920 may select the second division clock signalWCK/2_90 to be output as the second internal data clock signal IWCK/2_90in response to a logic high level of the first phase detection signalPDS_90. The second multiplexer 920 may select the fourth division clocksignal WCK/2_270 to be output as the second internal data clock signalIWCK/2_90 in response to a logic high level of the second phasedetection signal PDS_270.

The third multiplexer 930 may receive the third division clock signalWCK/2_180 through a first input terminal I1 and may receive through asecond input terminal 12 the first division clock signal WCK/2_0 whichis in a state where its phase is inverted by 180 degrees with respect tothe third division clock signal WCK/2_180. The third multiplexer 930 mayselect one signal from among the third division clock signal WCK/2_180and the first division clock signal WCK/2_0 to be output as the thirdinternal data clock signal IWCK/2_180 in response to the first andsecond phase detection signals PDS_90 and PDS_270.

The third multiplexer 930 may select the third division clock signalWCK/2_180 to be output as the third internal data clock signalIWCK/2_180 in response to a logic high level of the first phasedetection signal PDS_90. The third multiplexer 930 may select the firstdivision clock signal WCK/2_0 to be output as the third internal dataclock signal IWCK/2_180 in response to a logic high level of the secondphase detection signal PDS_270.

The fourth multiplexer 940 may receive the fourth division clock signalWCK/2_270 through a first input terminal I1 and may receive through asecond input terminal 12 the second division clock signal WCK/2_90 whichis in a state where its phase is inverted by 180 degrees with respect tothe fourth division clock signal WCK/2_270. The fourth multiplexer 940may select one signal from among the fourth division clock signalWCK/2_270 and the second division clock signal WCK/2_90 to be output asthe fourth internal data clock signal IWCK/2_270 in response to thefirst and second phase detection signals PDS_90 and PDS_270.

The fourth multiplexer 940 may select the fourth division clock signalWCK/2_270 to be output as the fourth internal data clock signalIWCK/2_270 in response to a logic high level of the first phasedetection signal PDS_90. The fourth multiplexer 940 may select thesecond division clock signal WCK/2_90 to be output as the fourthinternal data clock signal IWCK/2_270 in response to a logic high levelof the second phase detection signal PDS_270.

In the present embodiment, in response to a logic high level of thefirst phase detection signal PDS_90, the multiplexer circuit 740 mayreceive the first to fourth division clock signals WCK/2_0, WCK/2_90,WCK/2_180, and WCK/2_270 input through the respective first inputterminals I1 of the first to fourth multiplexers 910 to 940 to outputthe first to fourth internal data clock signals IWCK/2_0, IWCK/2_90,IWCK/2_180, and IWCK/2_270. In response to a logic high level of thesecond phase detection signal PDS_270, the multiplexer circuit 740 mayoutput the first to fourth internal data clock signals IWCK/2_0,IWCK/2_90, IWCK/2_180, and IWCK/2_270 each corresponding to a divisionclock signals which is in a state where its phase is inverted by 180degrees with respect to the division clock signal provided to its firstinput terminal I1.

FIGS. 10 and 11 are timing diagrams for describing an operation of aclock synchronizing circuit of FIG. 7, according to an exemplaryembodiment of the inventive concept. FIG. 10 is for describing amisaligned state in which clock synchronization is not made between themain clock signal CK and the data clock signal WCK. FIG. 11 is fordescribing an aligned state in which clock synchronization is madebetween the main clock signal CK and the data clock signal WCK. FIGS. 10and 11 will be described in reference to FIGS. 1, 5A, 5B, 6, 7, 8A, 8B,and 9.

Referring to FIG. 10, the main clock signal CK and the data clock signalWCK may be received by the memory device 120 (see FIG. 1).

The main clock signal CK having a clock cycle period of tCK may bereceived from a time Ta. A falling edge of the main clock signal CK maybe input at the time Ta, a rising edge of the main clock signal CK maybe input at a time Tb, a falling edge of the main clock signal CK may beinput at a time Tc, a rising edge of the main clock signal CK may beinput at a time Td, and a falling edge of the main clock signal CK maybe input at a time Te.

At the time Ta, the clock synchronization command CMD_SYNC may bereceived along with the clock signal CK.

The data clock signal WCK having a preamble period may be received fromthe time Tb. The data clock signal WCK may have a preamble period fromthe time Tb to the time Td and may have a data input/output period fromthe time Td. The preamble period of the data clock signal WCK may havethe same clock frequency as that of the main clock signal CK. The datainput/output period of the data clock signal WCK may have a clockfrequency which is twice the frequency of the main clock signal CK. Thedata clock signal WCK may be set to have a variable frequency (e.g., adynamic frequency) so that a frequency of the preamble period differsfrom that of data input/output period.

At the time Tb, the clock synchronization signal ISYNC may be generatedfrom the clock synchronization command CMD_SYNC synchronized with themain clock signal CK by the command decoder 610 (see FIG. 6). The firstto fourth division clock signals WCK/2_0, WCK/2_90, WCK/2_180, andWCK/2_270 may be generated from the data clock signal WCK by themulti-phase generator 720 (see FIG. 7).

The first division clock signal WCK/2_0 may have the same phase as thatof the division clock signal WCK/2, the second division clock signalWCK/2_90 may have a phase obtained through a 90-degree shift from thedivision clock signal WCK/2, the third division clock signal WCK/2_180may have a phase obtained through a 180-degree shift from the divisionclock signal WCK/2, and the fourth division clock signal WCK/2_270 mayhave a phase obtained through a 270-degree shift from the division clocksignal WCK/2.

At the time Tc, when the main clock signal CK has a falling edge, theclock synchronizing circuit 650 may latch the clock synchronizationsignal ISYNC in response to falling edges of the second and/or fourthdivision clock signals WCK/2_90 and WCK/2_270. For example, when a logiclevel of the clock synchronization signal ISYNC latched based on thefalling edge of the fourth division clock signal WCK/2_270 is logichigh, the clock synchronizing circuit 650 may output the second phasedetection signal PDS_270 having a logic high level. This represents amisaligned state where clock synchronization is not made between themain clock signal CK and the data clock signal WCK.

In response to the second phase detection signal PDS_270 having a logichigh level, the clock synchronizing circuit 650 may output the first tofourth internal data clock signals IWCK/2_0, IWCK/2_90, IWCK/2_180, andIWCK/2_270 corresponding to division clock signals which are in a statewhere a phase is inverted by 180 degrees with respect to each of thefirst to fourth division clock signals WCK/2_0, WCK/2_90, WCK/2_180, andWCK/2_270.

According to an exemplary embodiment of the inventive concept, at thetime Tc, the clock synchronizing circuit 650 may latch the clocksynchronization signal ISYNC in response to rising edges of the secondand/or fourth division clock signals WCK/2_90 and WCK/2_270.

The clock synchronizing circuit 650 may have an align margin including asetup time S of 0.5tCK and a hold time H of 0.5tCK when determining alogic level of the clock synchronization signal ISYNC in response to thefourth division clock signal WCK/2_270. Even when an align margin ismore strictly applied, the align margin may include a setup time S of0.25tCK and a hold time H of 0.25tCK.

Therefore, even when the align margin including the setup time S of0.25tCK and the hold time H of 0.25tCK is strictly applied, the memorydevice 120 secures twice the align margin in comparison with a setuptime S of 0.125tCK and a hold time H of 0.125tCK. Therefore, the memorydevice 120 secures an increased align margin when performing a clocksynchronizing operation by using the data clock signal WCK having thedynamic frequency.

Referring to FIG. 11, similar to FIG. 10, the main clock signal CKhaving a clock cycle period of tCK may be received from a time Ta, andthe data clock signal WCK having a preamble period may be received froma time Tb. At the time Tb, in response to the clock synchronizationcommand CMD_SYNC, the first to fourth division clock signals WCK/2_0,WCK/2_90, WCK/2_180, and WCK/2_270 may be generated from the data clocksignal WCK by the clock synchronizing circuit 650.

At a time Tc, when the main clock signal CK has a falling edge, theclock synchronizing circuit 650 may latch the clock synchronizationsignal ISYNC in response to falling edges of the second and/or fourthdivision clock signals WCK/2_90 and WCK/2_270. When a logic level of theclock synchronization signal ISYNC latched based on the falling edge ofthe second division clock signal WCK/2_90 is logic high, the clocksynchronizing circuit 650 may output the first phase detection signalPDS_90 having a logic high level. This represents an aligned state whereclock synchronization is made between the main clock signal CK and thedata clock signal WCK.

According to an exemplary embodiment of the inventive concept, at thetime Tc, the clock synchronizing circuit 650 may latch the clocksynchronization signal ISYNC in response to rising edges of the secondand/or fourth division clock signals WCK/2_90 and WCK/2_270.

In response to the first phase detection signal PDS_90 having a logichigh level, the clock synchronizing circuit 650 may output the first tofourth internal data clock signals IWCK/2_0, IWCK/2_90, IWCK/2_180, andIWCK/2_270 by using the first to fourth division clock signals WCK/2_0,WCK/2_90, WCK/2_180, and WCK/2_270.

The clock synchronizing circuit 650 may have an align margin including asetup time S of 0.5tCK and a hold time H of 0.5tCK when determining alogic level of the clock synchronization signal ISYNC in response to thesecond division clock signal WCK/2_90. Even when an align margin is morestrictly applied, the align margin may include a setup time S of 0.25tCKand a hold time H of 0.25tCK.

FIG. 12 is a flowchart for describing a clock synchronizing operationperformed by a memory device of FIG. 6, according to an exemplaryembodiment of the inventive concept.

Referring to FIG. 12 in association with FIG. 6, in operation S1210, thememory device 120 may receive the clock signal CK transmitted throughthe first clock signal line 11 (see FIG. 1) from the memory controller110 (see FIG. 1).

In operation S1220, the memory device 120 may receive the data clocksignal WCK transmitted through the second clock signal line 14 (seeFIG. 1) from the memory controller 110. The data clock signal WCK mayhave a preamble period before a time when the data DQ is input/output,and may be set to have a dynamic frequency so that a frequency of thepreamble period and a frequency of a data input/output period aredifferently set. In the data clock signal WCK, the preamble period maybe set to have the same clock frequency as that of the main clock signalCK, and the data input/output period may be set to have a clockfrequency which is twice the clock frequency of the main clock signalCK.

In operation S1230, the memory device 120 may receive a clocksynchronization command CMD_SYNC transmitted through the command bus 12(see FIG. 1) from the memory controller 110 (see FIG. 1). The memorydevice 120 may generate the clock synchronization signal ISYNC accordingto the clock synchronization command CMD_SYNC.

In operation S1240, the memory device 120 may generate the first tofourth division clock signals WCK/2_0, WCK/2_90, WCK/2_180, andWCK/2_270, based on the data clock signal WCK. The first division clocksignal WCK/2_0 may have a phase obtained by twice-dividing the dataclock signal WCK, the second division clock signal WCK/2_90 may have aphase obtained through a 90-degree shift from the first division clocksignal WCK/2_0, the third division clock signal WCK/2_180 may have aphase obtained through a 180-degree shift from the first division clocksignal WCK/2_0, and the fourth division clock signal WCK/2_270 may havea phase obtained through a 270-degree shift from the first divisionclock signal WCK/2_0.

In operation S1250, the memory device 120 may compare the clocksynchronization signal ISYNC with each of the second and fourth divisionclock signals WCK/2_90 and WCK/2_270 and may generate the first andsecond phase detection signals PDS_90 and PDS_270, based on a result ofthe comparison. In response to a falling edge of the second divisionclock signal WCK/2_90, the memory device 120 may determine a logic levelof the clock synchronization signal ISYNC to generate the first phasedetection signal PDS_90, and in response to a falling edge of the fourthdivision clock signal WCK/2_270, the memory device 120 may determine thelogic level of the clock synchronization signal ISYNC to generate thesecond phase detection signal PDS_270.

According to an exemplary embodiment of the inventive concept, inresponse to a rising edge of the second division clock signal WCK/2_90,the memory device 120 may determine the logic level of the clocksynchronization signal ISYNC to generate the first phase detectionsignal PDS_90, and in response to a rising edge of the fourth divisionclock signal WCK/2_270, the memory device 120 may determine the logiclevel of the clock synchronization signal ISYNC to generate the secondphase detection signal PDS_270.

In the memory device 120, when the logic level of the clocksynchronization signal ISYNC latched based on the second division clocksignal WCK/2_90 is logic high, the clock synchronizing circuit 650 mayoutput the first phase detection signal PDS_90 having a logic highlevel. In the memory device 120, when the logic level of the clocksynchronization signal ISYNC latched based on the fourth division clocksignal WCK/2_270 is logic high, the clock synchronizing circuit 650 mayoutput the second phase detection signal PDS_270 having a logic highlevel.

In operation S1260, the memory device 120 may generate the first tofourth internal data clock signals IWCK/2_0, IWCK/2_90, IWCK/2_180, andIWCK/2_270 according to the first and second phase detection signalsPDS_90 and PDS_270. In response to a logic high level of the first phasedetection signal PDS_90, the memory device 120 may receive the first tofourth division clock signals WCK/2_0, WCK/2_90, WCK/2_180, andWCK/2_270 and output them as the first to fourth internal data clocksignals IWCK/2_0, IWCK/2_90, IWCK/2_180, and IWCK/2_270, respectively.In response to a logic high level of the second phase detection signalPDS_270, the memory device 120 may output the first to fourth internaldata clock signals IWCK/2_0, IWCK/2_90, IWCK/2_180, and IWCK/2_270corresponding to division clock signals which are in a state where aphase is inverted by 180 degrees with respect to each of the first tofourth division clock signals WCK/2_0, WCK/2_90, WCK/2_180, andWCK/2_270. For example, the first internal data clock signal IWCK/2_0corresponds to the third division clock signal WCK/2_180, and the secondinternal data clock signal IWCK/2_90 corresponds to the fourth divisionclock signal WCK/2_270.

In operation S1270, the memory device 120 may use the first to fourthinternal data clock signals IWCK/2_0, IWCK/2_90, IWCK/2_180, andIWCK/2_270 which are generated in operation S1260, thereby ending aclock synchronizing operation between the main clock signal CK and thedata clock signal WCK.

Subsequently, the memory device 120 may perform a data writing operationand a data reading operation by using the first to fourth internal dataclock signals IWCK/2_0, IWCK/2_90, IWCK/2_180, and IWCK/2_270. In awrite operation, the memory device 120 may operate so that the writedata DQ input from the memory controller 110 is sampled by using thefirst to fourth internal data clock signals IWCK/2_0, IWCK/2_90,IWCK/2_180, and IWCK/2_270, and data obtained through the sampling iswritten in the memory cell array 632 by using the main clock signal CK.In addition, in a read operation, the memory device 120 may operate sothat data is read from the memory cell array 632 by using the main clocksignal CK, and the read data is transmitted to the memory controller 110by using the first to fourth internal data clock signals IWCK/2_0,IWCK/2_90, IWCK/2_180, and IWCK/2_270.

FIG. 13 is a block diagram illustrating an example where the memorydevice for performing a clock synchronizing operation according toexemplary embodiments of the inventive concept is applied to a mobiledevice 1300. The mobile device 1300 may be a mobile phone or asmartphone.

Referring to FIG. 13, the mobile device 1300 may include a global systemfor mobile communication (GSM) block 1310, a near field communication(NFC) transceiver 1320, an input/output (I/O) block 1330, an applicationblock 1340, a memory 1350, and a display 1360. It is to be understoodthat the mobile device 1300 illustrated in FIG. 13 may include more orfewer elements/blocks. In addition, in the present embodiment, GSMtechnology is illustrated as being used, but the mobile device 1300 maybe implemented by using other technologies such as code divisionmultiple access (CDMA). The elements/blocks of FIG. 13 may beimplemented as an integrated circuit (IC) type. Additionally, some ofthe elements/blocks may be implemented as an IC type, but otherelements/blocks may be implemented separately.

The GSM block 1310 may be connected to an antenna 1311 and may perform awireless phone operation in a known method. The GSM block 1310 mayinternally include a receiver and a transmitter and may performreception and transmission operations corresponding thereto.

The NFC transceiver 1320 may be configured to transmit or receive NFCsignals through inductive coupling for wireless communication. The NFCtransceiver 1320 may supply the NFC signals to an NFC antenna matchingnetwork system (NFC AMNS) 1321, and the NFC antenna matching networksystem (NFC AMNS) 1321 may transmit the NFC signals through theinductive coupling. The NFC antenna matching network system (NFC AMNS)1321 may receive NFC signals supplied from another NFC device and maysupply the received NFC signals to the NFC transceiver 1320.

Transmission and reception of the NFC signals by the NFC transceiver1320 may be performed in a time division manner. Therefore, a timeperiod where the NFC transceiver 1320 transmits the NFC signals may bereferred to as a “transmission period”, and a corresponding operationmode of the NFC transceiver 1320 may be treated as a “transmission mode”or an “NFC reader transmission mode”. Likewise, a time period where theNFC transceiver 1320 receives the NFC signals may be referred to as a“reception period”, and a corresponding operation mode of the NFCtransceiver 1320 may be treated as a “reception mode” or an “NFC tagreception mode”.

The NFC transceiver 1320 may operate according to rules standardized inECMA-340, ISO/IEC 18092, ETSI TS 102 190, ISO 21481, ECMA 352, and ETSITS 102 312 described in NFC interface and protocol-1 (NFCIP-1) and NFCinterface and protocol-2 (NFCIP-2).

The application block 1340 may include hardware circuits (for example,one or more processors) and may operate to provide various userapplications provided by the mobile device 1300. The user applicationsmay include voice call operations, data transmission, data swap, etc.The application block 1340 may operate along with the GSM block 1310and/or the NFC transceiver 1320 to provide the operation features of theGSM block 1310 and/or the NFC transceiver 1320. Additionally, theapplication block 1340 may include a program for a point of sale (POS).The program may provide a credit card purchase and payment functionusing a mobile phone, for example, a smartphone.

The display 1360 may display an image in response to display signalsreceived from the application block 1340. The image may be provided bythe application block 1340 or may be generated by a camera built intothe mobile device 1300. The display 1360 may internally include a framebuffer for temporarily storing pixel values and may be configured with aliquid crystal display screen along with relevant control circuits.

The I/O block 1330 may provide an input function to a user and mayprovide outputs which are to be received through the application block1340.

The memory 1350 may store programs (e.g., commands) and/or data whichare to be used by the application block 1340, and may be implementedwith random access memory (RAM), read-only memory (ROM), flash memory,and/or the like. Therefore, the memory 1350 may include non-volatilestorage devices as well as volatile storage devices. For example, thememory 1350 may correspond to the memory device 120 illustrated in FIG.6.

The memory 1350 may perform a clock synchronizing operation between afirst clock signal CK, supplied from a core circuit connected to amemory cell array, and a second clock signal WCK supplied from a datacircuit. The second clock signal WCK may be supplied whenever data isinput or output, may have a preamble period having a first clockfrequency before a time when the data is input or output, and may have asecond clock frequency different from the first clock frequency afterthe preamble period.

By using a command decoder, the memory 1350 may receive a clocksynchronization command during a preamble period of the second clocksignal WCK to generate a clock synchronization signal. By using adivider, the memory 1350 may divide the second clock signal WCK togenerate first to fourth division clock signals respectively havingphases obtained through 0-degree, 90-degree, 180-degree, and 270-degreephase shifts from an output of the divider. By using a clocksynchronizing circuit, the memory 1350 may latch the clocksynchronization signal in response to the second and fourth divisionclock signals, which are in a state where a phase is invertedtherebetween, among the first to fourth division clock signals. Based ona result of the latch, the memory 1350 may output the first to fourthdivision clock signals as internal data clock signals or may outputdivision clock signals, which are in a state where a phase is invertedby 180 degrees with respect to each of the first to fourth divisionclock signals, as the internal data clock signals.

While the inventive concept has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the inventive concept as definedby the following claims.

What is claimed is:
 1. A memory device, comprising: a first clockreceiver configured to receive a first clock signal; a second clockreceiver configured to receive a second clock signal when data is inputor output, wherein the second clock signal has a first clock frequencyin a preamble period, and has a second clock frequency different fromthe first clock frequency after the preamble period; a command decoderconfigured to receive a clock synchronization command synchronized withthe first clock signal and generate a clock synchronization signal,wherein the clock synchronization signal is generated during thepreamble period; and a clock synchronizing circuit configured togenerate a plurality of division clock signals in response to the secondclock signal, latch the clock synchronization signal during the preambleperiod, and selectively provide the plurality of division clock signalsas internal data clock signals according to a result of the latching,wherein the clock synchronization signal is provided to a data input ofa flip flop and latched in response to one of the division clock signalsprovided to a clock input of the flip flop.
 2. The memory device ofclaim 1, wherein the first clock frequency of the second clock signal isa same as a frequency of the first clock signal.
 3. The memory device ofclaim 1, wherein the first clock frequency of the second clock signalhas is different from a frequency of the first clock signal.
 4. Thememory device of claim 1, wherein the second clock frequency of thesecond clock signal is higher than the first clock frequency of thesecond clock signal.
 5. The memory device of claim 1, wherein the memorydevice is configured to input or output the data after the preambleperiod.
 6. The memory device of claim 1, wherein the clocksynchronization circuit comprises: a multi-phase generator configured togenerate first to fourth division clock signals, wherein each of thedivision clock signals is phase shifted with respect to the second clocksignal; a first phase detector configured to latch the clocksynchronization signal to output a first phase detection signal inresponse to one of two division clock signals having inverted phaseswith respect to each other; a second phase detector configured to latchthe clock synchronization signal to output a second phase detectionsignal in response to the other of the two division clock signals havinginverted phases with respect to each other; and a multiplexer circuitconfigured to output the first to fourth division clock signals as firstto fourth internal data clock signals, respectively, in response to thefirst and second phase detection signals, or to output the third,fourth, first and second division clock signals as the first to fourthinternal data clock signals, respectively, in response to the first andsecond phase detection signals.
 7. The memory device of claim 6, whereinthe multi-phase generator is configured to divide the second clocksignal and generate the first division clock signal through a 0-degreephase shift from the divided second clock signal, the second divisionclock signal through a 90-degree phase shift from the divided secondclock signal, the third division clock signal through a 180-degree phaseshift from the divided second clock signal, and the fourth divisionclock signal through a 270-degree phase shift from the divided secondclock signal.
 8. A clock synchronizing method performed by a memorydevice, the clock synchronizing method comprising: receiving a firstclock signal; receiving a second clock signal which has a first clockfrequency in a preamble period before a time when data is input oroutput, and has a second clock frequency different from the first clockfrequency after the preamble period; receiving a clock synchronizationcommand synchronized with the first clock signal and generating a clocksynchronization signal during the preamble period; dividing the secondclock signal and generating a plurality of division clock signals;latching the clock synchronization signal at a flip flop in response toa division clock signal provided to the flip flop, wherein the divisionclock signal is selected from among the plurality of division clocksignals; and selectively outputting the plurality of division clocksignals as internal data clock signals according to a result of thelatching.
 9. The clock synchronizing method of claim 8, wherein thesecond clock signal is received when the data is input to or output fromthe memory device.
 10. The clock synchronizing method of claim 8,wherein the dividing of the second clock signal comprises: dividingtwice, by a divider, the second clock signal; and generating the firstdivision clock signal obtained through a 0-degree phase shift from anoutput of the divider, a second division clock signal obtained through a90-degree phase shift from the output of the divider, a third divisionclock signal obtained through a 180-degree phase shift from the outputof the divider, and a fourth division clock signal obtained through a270-degree a phase shift from the output of the divider.
 11. The clocksynchronizing method of claim 10, wherein the latching of the clocksynchronization signal comprises: latching the dock synchronizationsignal and outputting a first phase detection signal in response to thesecond division clock signal; and latching the clock synchronizationsignal and outputting a second phase detection signal in response to thefourth division clock signal.
 12. The clock synchronizing method ofclaim 11, wherein the selectively outputting of the plurality ofdivision clock signals comprises: outputting the first division clocksignal as a first internal data clock signal in response to the firstphase detection signal; outputting the second division clock signal as asecond internal data clock signal in response to the first phasedetection signal; outputting the third division clock signal as a thirdinternal data clock signal in response to the first phase detectionsignal; and outputting the fourth division clock signal as a fourthinternal data clock signal in response to the first phase detectionsignal.
 13. The clock synchronizing method of claim 11, wherein theselectively outputting of the plurality of division clock signalscomprises: outputting the third division clock signal as a firstinternal data clock signal in response to the second phase detectionsignal; outputting the fourth division clock signal as a second internaldata clock signal in response to the second phase detection signal;outputting the first division clock signal as a third internal dataclock signal in response to the second phase detection signal; andoutputting the second division clock signal as a fourth internal dataclock signal in response to the second phase detection signal.
 14. Amemory system, comprising: a memory controller configured to output acommand, a main clock signal and a data clock signal; and a memorydevice configured to generate a clock synchronization signal in responseto the command from the memory controller, and synchronize the mainclock signal with the data clock signal during a first period of thedata clock signal, wherein a frequency of the data clock signal duringthe first period is slower than a frequency of the data clock signalduring a second period after the first period, wherein the clocksynchronization signal is compared with one of a second divided dataclock signal and a fourth divided data clock signal to generate a phasedetection signal.
 15. The memory system of claim 14, wherein the commandoutput from the memory controller is a read command, a write command ora synch command.
 16. The memory system of claim 14, wherein when afalling edge of the second divided data clock signal coincides with ahigh level of the clock synchronization signal, a first divided dataclock signal and the main clock signal are aligned in the first period.17. The memory system of claim 14, wherein when a rising edge of thefourth divided data clock signal coincides with a high level of theclock synchronization signal, a first divided data clock signal and themain clock signal are aligned in the first period.
 18. The memory systemof claim 14, wherein the data clock signal and the main clock signalhave a different frequency from each other during the second period ofdata clock signal.
 19. The memory system of claim 14, wherein data isread to or written from the memory device during the second period ofthe data clock signal.
 20. The memory system of claim 14, wherein thefirst period of the data clock signal is a preamble period.